By John Burrows, P.Eng.
The 2010 editions of the National Model Construction Codes—the National Building Code of Canada (NBC), the National Fire Code of Canada (NFC), and the National Plumbing Code of Canada (NPC)—were released last November. Published by the National Research Council Institute for Research in Construction (NRC-IRC), the new codes contain about 800 technical changes.
The revisions are the result of a five-year collaboration between the Canadian Commission on Building and Fire Codes (CCBFC), the provinces and territories, the construction industry, and the public. This article focuses primarily on the most significant changes. (More detailed information about these code changes—and many more not mentioned in this article—can be found in presentations that are available at www.nationalcodes.ca/eng/presentations/2010_codes_presentations.shtml. Emergency changes were also published for the NBC in June. NRC also released a new edition of the National Energy Code of Canada for Buildings 2011).
Structural safety
The 2010 edition of NBC has changed requirements in Part 4, “Structural Design,” for live loads due to use and occupancy. A new load combination table has been added for cranes to ensure design adequacy when acting in concert with other loads.
The minimum live loads for arenas, grandstands, and stadiums having fixed seats with backs were reduced to reflect the fact this seating arrangement discourages overcrowding and overloading that can result where there is moveable seating or bleachers. The same principle was applied to churches, lecture halls, and theatres that have fixed seats with backs. Guard-loading has been revised for open viewing stands, where spectators are not restricted by fixed seating from crowding a guard. More weight-specific loads were introduced for live and concentrated loads for garages.
For wind design, Part 4 now requires very tall buildings be designed using experimental methods (e.g. wind tunnel testing). Buildings 60 m (197 ft) or higher require dynamic analysis.
Safety issues for Part 9, “Housing and Small Buildings,” structures began to arise with the trend of ‘open-concept construction,’ such as the practice of building on narrow lots and use of big windows, particularly in areas where exposure to wind and earthquakes is high. This type of construction meant there could be inadequate strength to resist the lateral loads from windstorms or seismic activity.
To address this problem, new requirements for bracing and lateral load resistance were added to Part 9 based on three levels of risk:
- low to moderate;
- high; and
- extreme.
Buildings in the first category have resistance to wind and earthquake loads by virtue of traditional wood-frame construction composed of exterior sheathing, panel-type cladding, or gypsum board finish.
Photos courtesy NRC-IRC
Buildings in the high exposure category require additional features to provide required resistance to lateral loads. Of all the locations identified in NBC Appendix C, six fall into this category for wind and 45 for earthquakes. For wind, areas in Newfoundland, Alberta, and the Northwest Territories are impacted. Of the locations affected by seismic risk, most are located in the coastal region of British Columbia, but three are in the Lower St. Lawrence region of Québec.
For these areas, prescriptive requirements have been added to Part 9 so builders can incorporate adequate lateral load resistance without the need for further structural engineering design. These include constructing walls using ‘braced wall panels’ in ‘braced wall bands’ that are continuous horizontally and vertically throughout the building.
The panels and bands extend from the top of the supporting foundation, slab, or sub-floor to the roof framing above.
The requirements specify the number and type of walls needed and the spacing and materials that can be used. There is also the option of obtaining an engineered design based on Part 4.
Buildings in the extreme exposure category must be engineered according to Part 4, or to the Canadian Wood Council’s (CWC’s) Engineering Guide for Wood Frame Construction. Of all the locations identified in NBC Appendix C, only one location—in Nunavut—falls into this category for wind; there are three locations for earthquake exposure, all in Québec’s Upper St. Lawrence region.
Fire safety
New buildings falling under NBC Parts 3, “Fire Protection, Occupant Safety, and Accessibility,” and 9 now require exit signs to be in pictogram form, green on white. The requirement follows International Organization for Standardization (ISO) standards:
- colour specifications: ISO 3864-1, Graphical Symbols: Safety Colours and Safety Signs–Part 1: Design principles for safety signs and safety markings; and
- dimensions: ISO 7010, Graphical Symbols: Safety Colours and Safety Signs: Safety signs used in workplaces and public areas.
Unlike the old format, using red lettering that read “Exit/Sortie” on a white background, the new signage is not dependent on literacy; it is an easily discerned ‘running man’ image and directional arrows. This change—Underwriters Laboratories of Canada (CAN/ULC) S572-10, Photoluminescent and Self-luminous Exit Signs and Path Marking Systems—reflects the international trend for exit signs and is more universally recognized.
Photo © BigStockPhoto/Natalia Bratslavsky
Measures have been introduced in Parts 3 and 9 to improve fire safety in residential occupancies. In addition to the requirements for interconnected smoke alarms on each storey of a residential occupancy, interconnected smoke alarms must now be installed in each bedroom. These smoke alarms must be equipped with a battery backup in addition to being hardwired.
NBC has added definitions and clarifications to Parts 3 and 9 to improve the understanding of fire stops and fire blocks and the importance of sealing pipe and duct penetrations through fire separations. Cables placed within plenum spaces will require either an FT4 or FT6 rating depending on whether the building is made of combustible or noncombustible construction, respectively. (The higher FT rating relates to a lower flame spread and smoke development classification.) New requirements have been introduced for the protection of conductors serving life safety systems, including:
- fire alarms;
- emergency lighting;
- smoke control;
- elevators; and
- fire pumps.
A number of fires that impacted multiple homes and buildings led to new requirements in Parts 3 and 9 to prevent the spread of flames from one building to another. These changes clarify fire department response time assumptions and under certain conditions limit the:
- number and size of unprotected openings;
- cladding type that can be used; and
- degree to which soffits may overhang buildings.
Another safety issue is openable windows in high-rise residential buildings, as they can pose a potential falling hazard, especially for children. This has led to new code requirements in Part 3 intended to limit the likelihood of falls. One safety option is a guard 1070 mm (42 in.) high, on the front of windows. The other is a limiter that restricts the opening of a window to no more than 100 mm (4 in.).
